The present invention relates to a valve actuating mechanism for opening and closing an intake or exhaust valve of an internal combustion engine installed on a vehicle.
Conventionally, a valve actuating mechanism for internal combustion engines as shown in FIG. 1 is known in which a rotating cam 1 has its camming surface 2 disposed to slide on a cam slipper surface 4 of a rocker arm 3 to thereby open and close an intake valve 5 (or exhaust valve 6) by rocking motion of the rocker arm 3.
This type of valve actuating mechanism is required to have so high wear resistance that it is not adversely affected by lubricating conditions which may vary according to the type of lubricating oil used and running conditions of the vehicle, as well as to be light in weight to contribute to grading up the performance of the engine.
However, the conventional valve actuating mechanism has the disadvantage that the camming surface 2 and the cam slipper surface 4 are liable to wear, which makes it impossible to meet the above requirements.
Analysis of the cause of the wear has revealed that, in almost all cases, the wear is caused by scuffing due to breakage of the oil film. Breakage of the oil film can cause scuffing and sometimes even seizure even if the pressure or load acting upon the camming surface 2 and/or the cam slipper surface 4 is reduced, which, therefore, cannot completely solve the problem.